Synthesis, single crystal X-ray structure and optical properties of 3,4-dimethyl-dithieno[2,3-b:3',2'-d]thiophene-7,7-dioxide

The synthesis of the title compound ( 4 ), starting from commercial 3-bromo-4-methylthiophene, is described. The single crystal packing mode of 4 , as well as the absorption and photoluminescence properties in solution and in the solid state are reported and analyzed in relation to those of the isomeric 3,5-dimethyl-dithieno[3,2-b:2′,3′-d]thiophene-4,4-dioxide ( 7 ). The different reactivities of 4 and 7 towards bromination are analyzed in the light of the results of ab initio B3LYP/6-31G∗ calculations on both compounds.